1) Field of the Invention
The present invention relates to a process for producing a polycarbonate resin with both good transparency and good color which is not colored during its production.
2) Prior Art
A polycarbonate resin obtained by melt polycondensation of pentacyclopentadecanedimethanol represented by the general formula (1) and/or the general formula (2) with carbonic acid diester, as shown in Japanese Patent Kokai (Laid-open) No. 2000-302860, is excellent in transparency, heat resistance, impact resistance and possesses a low photoelastic constant and a good balance between refractive index and Abbe""s number. 
Thus, this polycarbonate resin is suitably applicable to plastic optical products such as optical disc substrates, various lenses, prisms, optical fibers and photoconductive boards.
However, when a catalyst such as basic compounds including alkaline metal compounds, alkaline earth metal compounds and nitrogen- or phosphorus-containing compounds described in Japanese Patent Kokai (Laid-open) No. 2000-302860 was used in the production, there caused problems that it was difficult to obtain a polycarbonate resin product with good color since the polycarbonate resin was readily colored during melt polycondensation.
A polycarbonate resin obtained by melt polycondensation of petacyclopentadecanedimethanol represented by the general formula (1) and/or the general formula (2) and alicyclic diol represented by the general foumula (4) with carbonic acid diester, as shown in Japanese Patent Kokai (Laid-open) No. 2001-11168, is excellent in transparency, heat resistance, flowability and possesses a low photoelastic constant and a good balance between refractive index and Abbe""s number. 
Thus, this polycarbonate resin is suitably applicable to plastic optical products such as optical disc substrates, various lenses, prisms, optical fibers and photoconductive boards.
However, when a catalyst such as basic compounds including alkaline metal compounds, alkaline earth metal compounds and nitrogen- or phosphorus-containing compounds described in Japanese Patent Kokai (Laid-open) No. 2001-11168 was used in the production, there caused problems that it was difficult to obtain a polycarbonate resin product with good color since the polycarbonate resin was readily colored during melt polycondensation.
A polycarbonate resin obtained by melt polycondensation of pentacyclopentadecanedimethanol represented by the general formula (1) and/or the general formula (2) and alicyclic diol represented by the general formula (5) with carbonic acid diester, as shown in Japanese Patent Kokai (Laid-open) No. 2001-11166, is excellent in transparency, heat resistance, flowability and possesses a low photoelastic constant and a good balance between refractive index and Abbe""s number. 
Thus, this polycarbonate resin is suitably applicable to plastic optical products such as optical disc substrates, various lenses, prisms, optical fibers and photoconductive boards.
However, when a catalyst such as basic compounds including alkaline metal compounds, alkaline earth metal compounds and nitrogen- or phosphorus-containing compounds described in Japanese Patent Kokai (Laid-open) No. 2001-11166 was used in the production, there caused problems that it was difficult to obtain a polycarbonate resin product with good color since the polycarbonate resin was readily colored during melt polycondensation.
A polycarbonate resin obtained by melt polycondensation of pentacyclopentadecanedimethanol represented by the general formula (1) and/or the general formula (2) and alicyclic diol represented by the general formula (6) with carbonic acid diester, as shown in Japanese Patent Kokai (Laid-open) No. 2001-11165, is excellent in transparency, heat resistance, flowability and possesses a low photoelastic constant and a good balance between refractive index and Abbe""s number. 
Thus, this polycarbonate resin is suitably applicable to plastic optical products such as optical disc substrates, various lenses, prisms, optical fibers and photoconductive boards.
However, when a catalyst such as basic compounds including alkaline metal compounds, alkaline earth metal compounds and nitrogen- or phosphorus-containing compounds described in Japanese Patent Kokai (Laid-open) No. 2001-11165 was used in the production, there caused problems that it was difficult to obtain a polycarbonate resin product with good color since the polycarbonate resin was readily colored during melt polycondensation.
A polycarbonate resin obtained by melt polycondensation of pentacyclopentadecanedimethanol represented by the general formula (1) and/or the general formula (2) and alicyclic diol represented by the general formula (7) with carbonic acid diester, as shown in Japanese Patent Kokai (Laid-open) No. 2001-11169, is excellent in transparency, heat resistance, flowability and possesses a low photoelastic constant and a good balance between refractive index and Abbe""s number. 
Thus, this polycarbonate resin is suitably applicable to plastic optical products such as optical disc substrates, various lenses, prisms, optical fibers and photoconductive boards.
However, when a catalyst such as basic compounds including alkaline metal compounds, alkaline earth metal compounds and nitrogen- or phosphorus-containing compounds described in Japanese Patent Kokai (Laid-open) No. 2001-11169 was used in the production, there causes problems that it was difficult to obtain a polycarbonate resin product with good color since the polycarbonate resin was readily colored during melt polycondensation.
An object of the present invention is to solve the above-mentioned prior art problems and to provide a process for producing a polycarboante resin with good transparency and good color which is not colored during its production.
As a result of extensive studies to solve the above-mentioned prior art problems, the inventors have found that the above-mentioned problems can be solved by a process for producing a polycarbonate resin which comprises performing melt polycondensation of pentacyclopentadecanedimethanol represented by the following general formula (1) and/or the following general formula (2) or pentacyclopentadecanedimethanol represented by the general formula (1) and/or the general formula (2) and diol represented by the following general formula (3) with carbonic acid diester in the presence of a catalyst containing at least one compound selected from the group consisting of zinc compounds, tin compounds, lead compounds, zirconium compounds and hafnium compounds; 
wherein X is an alkylene group having 3 to 14 carbon atoms or a cycloalkylene group having 4 to 14 carbon atoms, and have accomplished the present invention.
The present invention will be described in more detail below.
Pentacyclopentadecanedimethanol represented by the general formula (1) and/or the general formula (2) is hereinafter abbreviated as xe2x80x9cPCPDMxe2x80x9d.
Examples of diol represented by the general formula (3) include tricyclo(5.2.1.02,6) decanedimethanol, norbornane dimethanol, decaline-2,6-dimethanol, cyclohexane-1,4-dimethanol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol, 1,13-tridecanediol and 1,14-tetradecanediol.
The molar ratio (diol/PCPDM) of diol represented by the general formula (3) to PCPDM is preferably 0 to 2.3 from the aspect of heat resistance and more preferably 0 to 1. PCPDM, tricyclo(5.2.1.02,6) decanedimethanol, norbornane dimethanol, decaline-2,6-dimethanol and cyclohexane-1,4-dimethanol include all isomers thereof in the range of their structural formulas. Further, it is preferable that all the diols to be used have a high purity as much as possible.
As the catalyst to be used in the present invention, least one compound selected from the group consisting of zinc compounds, tin compounds, lead compounds, zirconium compounds and hafnium compounds is used. As the form of these compounds, oxide, halogenide, carboxylate, acetylacetonate, phenoxide, alkoxide and hydride, which are used alone or in the combination of plural compounds, are exemplified.
Preferable examples of the catalyst to be used in the present invention include at least one compound selected from the group consisting of the general formulas ZnY2, SnY2, SnY4, R2SnO, R2SnY2, R2Sn(ORxe2x80x2)2, PbY2, PbY4, ZrOY2, ZrY4, Zr(OR)4, HfY4 and Hf(OR)4 in which Y is a halogen atom, a carboxyl group having 1 to 18 carbon atoms, an acetylacetonate group or a hydrogen atom and R and Rxe2x80x2 are, each independently, an alkyl group having 1 to 4 carbon atoms or an aryl group having 6 to 10 carbon atoms.
More preferable examples of the catalyst include zinc acetate, zinc benzoate, zinc acetylacetonate, stannous acetate, stannic choride, dibutyltin oxide, dibutyltin dilaurate, dibutyltin dimethoxide, lead(II) acetate, zirconium oxyacetate, zirconium acetylacetonate, zirconium chloride, zirconium phenoxide, zirconium butoxide and hafnium acetylacetonate.
The amount of the catalyst is preferably 10xe2x88x929 to 10xe2x88x923 mol and more preferably 10xe2x88x928 to 10xe2x88x925 mol to sum total 1 mole of pentacyclopentadecanedimethanol represented by the general formula (1) and/or the general formula (2) and diol represented by the general formula (3).
Examples of carbonic acid diester to be used in the present invention include diphenyl carbonate, ditolyl carbonate, ethylphenyl carbonate, dinaphthyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, dibutyl carbonate and dicyclohexyl carbonate, among which diphenyl carbonate is preferable.
The amount of carbonic acid ester is preferably 0.97 to 1.10 mol and more preferably 0.99 to 1.04 mol to sum total 1 mole of pentacyclopentadecanedimethanol represented by the general formula (1) and/or the general formula (2) and diol represented by the general formula (3).
The melt polycondensation in the present invention can be performed by known processes. That is, pentacyclopentadecanedimethanol represented by the general formula (1) and/or the general formula (2), or pentacyclopentadecane dimethanol represented by the general formula (1) and/or the general formula (2) and diol represented by the general formula (3), carbonic acid diester and the catalyst are mixed with stirring and then melt polycondensation is performed while removing by-products under atmospheric pressure or a reduced pressure with heating. The reaction is usually performed in multi stage step of two stages or above.
In detail, the first stage reaction is performed at 120 to 260xc2x0 C. and preferably at 180 to 240xc2x0 C. for 0.1 to 5 hours and preferably for 0.3 to 3 hours. Then, the reaction temperature is raised while increasing a reduced pressure of the reaction system to perform the reaction of diol with carbonic acid diester. Finally, melt polycondensation is performed under a reduced pressure of 1 mmHg or below at a temperature of 200 to 300xc2x0 C. It is preferable that total reaction time is 2 to 9 hours. Such reaction may performed continuously or batch wise.
The present invention will be described in more detail below, referring to Examples, which are not intended to limit the scope of the present invention.
The properties of a resin were measured according to the following methods. [Weight average molecular weight based on polystyrene standard]
The measurement was made by GPC (gel permeation chromatography) using chloroform as a developing solvent. In more detail, a calibration curve of molecular weight-retention time was drawn up using polystyrene with known molecular weight by GPC and weight average molecular weight based on polystyrene standard was calculated based on the calibration curve.
Yellow Index (YI)
A pressed test piece of diameter 40 mmxc3x97thickness 3 mm was prepared and the measurement was made with a color-difference meter according to JIS K 7103 and JIS Z 8722.